The present invention relates to an apparatus for digital position measurements, comprising a cyclic position transducer which is supplied with a sinusoidal signal in order to provide at the output a pair of signals which are proportional to the sine and to the cosine of the angle corresponding to the position of measurement within the cycle of the transducer.
These apparatuses generally employ a transducer comprising a scale, provided with a single circuit in the form of a zig-zag with a predetermined elementary interval which defines the cycle of the transducer, and a cursor provided with two windings which are out of phase with respect to each other by a quarter of an elementary step. Normally these windings are supplied with signals which are proportional to the sine and the cosine, and which are generated by digital counters and digital-analog converters. The output signal on the scale, which corresponds to the error, i.e. to the difference between the position, or spot height, provided by the counters and the real position causes the counters to progress in order to reduce the error. These apparatuses have the disadvantage that the counters provide the real position with a certain delay with respect to the actual instant at which this position is reached. This is of particular disadvantage where dynamic indications of the position are being provided, since the greater the velocity of displacement, the greater the error must be, or in other words the difference between the instantaneous position indicated and the real position.
Measuring apparatuses are also known, in which the scale is supplied with a sinusoidal signal, whilst the output from the cursor consists of a pair of signals which are proportional to the sine and to the cosine of the angle within the cycle of the transducer corresponding to the position to be measured. These signals are employed for generating an error signal with respect to the position provided by a counter, as a result of which these apparatuses also suffer from the disadvantages indicated above.